1. Field of the Invention
The present invention relates to pharmaceutical compositions. In particular, this invention relates to pharmaceutical compositions formulated so that fluoroquinolone antibiotic drugs and xanthan gum are compatible.
2. Description of Related Art
Xanthan gum is a polysaccharide known to be useful in ophthalmic compositions as a viscosity-enhancing agent. U.S. Pat. No. 4,136,177 discloses ophthalmic compositions containing an ophthalmic drug and from about 0.01 to 2.5% (w/v) of xanthan gum. The '177 patent teaches that if the concentration of xanthan gum is from about 0.02 to about 1.0% (w/v), the composition is suitable for "dropwise" ophthalmic applications. In contrast, at concentrations of xanthan gum above about 1.0% and up to about 2.5% (w/v), "a gel-like consistency is attained." Thus, the '177 patent discloses compositions that are formulated to be either non-gelled liquids or gels before instillation in the eye. The '177 patent does not describe any xanthan gum-containing compositions as capable of being administered as a liquid and gelling upon contact with the eye. According to the '177 patent, any ophthalmic drug can be added to the xanthan gum-containing compositions, but the '177 patent does not include a fluoroquinolone antibiotic drug when it lists suitable antibacterial drugs (see Col. 3, lines 54 -58).
WO 99/51273 discloses gel-forming compositions containing xanthan gum where the xanthan gum has an initial bound acetate content of at least about 4% and an initial bound pyruvate content of at least about 2.5%. The entire contents of WO 99/51273 are hereby incorporated by reference.
Ciprofloxacin is an antibiotic drug known to be useful in pharmaceutical compositions. Because of solubility limitations, topically administrable aqueous compositions containing 0.3% (w/w) ciprofloxacin are generally formulated at low pH (e.g., pH 4.5) in order to avoid ciprofloxacin precipitating out of the composition. U.S. Pat. No. 5,679,336 discloses topically administrable pharmaceutical compositions formulated as solutions at or near physiological pH using polystyrene sulfonic acid.
Adding 0.3% (w/w) ciprofloxacin to a simple aqueous xanthan gum-containing composition, even at a pH of 4.5, causes a precipitate to form between ciprofloxacin and xanthan gum.